Prior art patent document published US 2005/0139268 A1 discloses a tap for gas cylinder and with a position indicator. The latter is mounted between a cylindrical portion of the tap body and the actuating wheel of the tap. The position indicator comprises, essentially, a sleeved-shaped support slip on the cylindrical portion of the tap body and an indicator sleeve with an inner thread engaging with an outer thread on the support. The indicator sleeve is also in rotational engagement with the actuating wheel of the tap. The sleeve-shaped support comprises a signalling end portion that can be covered and uncovered by the indicator sleeve. During operation of the tap, when rotating the actuating wheel, the indicator sleeve is rotated and, by virtue of the thread engagement with the support, can move up and down to uncover and cover, respectively, the signalling end portion of the support. This indicator is interesting by its simplicity. It shows however as drawback that the position of the indicator sleeve is linear with the rotation angle of the actuating wheel. In other words, a tap that is opened by a limited rotation angle, for example of an angle comprised between 50° and 90°, will not show a clear indication that the tap is opened whereas for many applications the gas will flow almost as if the tap was fully opened.
Prior art patent document published DE 10 2005 015 342 A1 discloses a visual indicator of the sense of rotation of the last manipulation of the spindle of a valve. The indicator comprises a rotation ring that is in rotational engagement with the spindle, a movement transmission ring with sloped slots and an indicator ring. The rotation ring comprises pins that engage with the sloped slots of the movement transmission ring and with the indicator ring so that upon rotation of the spindle, the indicator ring moves up or down thanks to the pins sliding along the sloped slots. The rotation ring is only frictionally engaged with the spindle, meaning the spindle can rotate relative to said ring when the pins are at the end of the slots. Also the slots are generally straight presumably because they are intended to provide a rapid movement of the indicator ring in response to the rotation of the spindle, bearing in mind that the spindle can be further rotated when the indicator reaches one of its two end positions.
None of these two teachings provides a position indicator that permits a rapid change in the position or status indication and that provides a reliable indication of the opening and/or closing status after several actuations of the valve or tap.